These directories let us know that in 1871, John E. Shackford of St Louis was working as a clerk and living at 904 Barlow Street and in 1873 he was working for J. C. Gerdes & Co and living at the same residence. And in the 1873 directory, we find a James A. Shackford, salesman at Hoblitzette & Cousland residing at 1309 Washington Av. We know the John E Shackford was the son of William Moore and Joanna (Chauncy) Shackford born in 1825 and died in 1873.
We need to do more research to identify the identity of the James A. Shackford - there is a possibility it is John's son from a first marriage although his name was James M. Shackford (1853-1928). This James was in Manchester NH in 1870 but married in Illinois in 1877. He would have been 20 so there is a chance he went out to St Louis in 1873 but we need a more proof before identifying if this is the correct James Shackford.
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1873 Gould's Directory (N.p.:n.p., 1873), page 775, John E Shackford; digtal image, Missouri Digital Heritage (: accessed 27 April 2015).
Edwards' Thirteenth Annual Director to the Inhabitants, Institutions, Incorporated Companies, Business, Business Firms, Manufacturing Establishments, Etc., in the City of Saint Louis, for 1871 (N.p.:n.p., 1871), page 600, John E Shackford; digital images, Missouri Digital Heritage (: accessed 27 April 2015).